| The chemical properties and surface structure of the solid surface have a great influence on the wetting behavior.Many studies have demonstrated that the effect of surface chemistry on wettability is limited.Therefore,it is crucial to design surfaces with micro/nano structure to improve the surface wettability,which prompting researchers to design a variety of structures to meet their needs.At the same time,the effect of external fields is ubiquitous,such as light,temperature,electricity,etc.,which also provides ideas for actively adjusting the surface wettability.According to the Wenzel equation,the surface roughness amplifies the original wettability of the surface.However,the surface with cavity structures can trap part of the air in the cavity,thereby resisting the penetration of droplets into the cavity,which is a major factor in the wettability of the surface.Under this condition,it is possibility that achieve the hydrophobic properties on hydrophilic surface.And the previous researches focused on the influence of single structural parameter of micro/nano structure unit on wettability,while the joint influence of multiple structural parameters on wettability was almost not discussed.Therefore,the influence mechanism of trapezoidal cavity structure and external field on surface wettability are studied in our research through molecular dynamics.The results of our research provide support for the preparation of superhydrophobic surfaces and the control of wettability.The main research contents and results of the research are as follows:(1)In order to explore the effect of surface micro/nano structure on wettability,several wetting models with different trapezoidal cavities are established,the contact angles and contact states under different trapezoidal cavity structures are discussed.The role of trapezoidal cavity depth and bottom edge in joint control of wettability is summarized.And the effect of the upper base angle of the trapezoidal cavity on the delay of contact state transition is also analyzed.Finally,the Cassie-Baxter equation is modified.(2)The wetting models with different micro/nano structures surface are established,and the influence mechanism of rough surfaces on wettability is explored through molecular dynamics simulations.First,the droplets are layered by the one-dimensional density curve of the droplets,and then the distribution of intermolecular hydrogen bond grids,the arrangement of water molecules,and the radial distribution function in different droplet layers are systematically analyzed,respectively.The difference of the influence of rough structure on different water layers is found,the results can explain the influence of surface roughness on wettability at the atomic scale.(3)Based on the rough surface with trapezoidal cavities,and the diffusion and permeation behaviors of droplets at different impact velocities were simulated.The relationship between the maximum spreading factor,the time and height of the lowest point of the centroid and the impact velocity are obtained,and we also find that the change of the cavity structure did not affect the scaling law of the maximum spreading factor of the droplet.At the same time,the impact dynamics of droplets under different trapezoidal cavity structures are also studied.And the joint effect mechanism of the upper edge and depth of the trapezoidal cavity on the impact behavior of the droplet is obtained.Finally,a model describing the maximum spreading factor of droplets on the surface with trapezoidal cavity structure is proposed based on the principle of energy conservation.(4)The wettability on the vibrating monolayer graphene were studied.The contact states of the droplets on the vibrating substrate surface and the relationship between the contact states and the amplitude of the substrate are discussed,respectively.Then,several wetting systems are established to describe the wetting behavior of nanofluid droplets on the vertical vibrating surface by adjusting the number of nanoparticles and the hydrophilicity of nanoparticles.The research shows that vibration can be used as a potential method to adjust the surface wettability reversibly.(5)The condensation behavior of water vapor under the action of constant electric fieldand alternative electric field parallel to the surface is studied.By calculating the critical nucleus,nucleation time,growth process of the largest cluster and condensation efficiency during the condensation,the role of the strength of the constant electric field and the frequency of the alternating electric field in regulating the condensation of water vapor is quantitatively and systematically expounded.The results show that the electric field will have a significant impact on the growth direction and size of the cluster.Finally,the regulation mechanism of electric field on water vapor condensation is explained in detail from the aspects of mean square displacement,distribution of water molecule dipole moment and water molecule temperature. |
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